.header {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 200px;
  height: 200px;
  background-color: pink;
}
.header a {
  width: 50px;
  height: 50px;
  color: #fff;
  background-color: black;
  line-height: 50px;
  text-align: center;
  font-size: 18px;
}
.header a:hover {
  background-color: purple;
}
.nav {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 200px;
  height: 200px;
  background-color: blue;
}
.nav .nav-hd {
  width: 50px;
  height: 50px;
  font-size: 18px;
  line-height: 50px;
  color: #fff;
  text-align: center;
  background-color: green;
}
